The background of the present invention may be summarized in one word: “wires”. Most stored program controlled systems of even minor complexity consist of a plurality of single or limited functionality processing units, each of which is connected to one or more of the other processing units by wires. There are literally millions of miles of interconnecting wires in current use in systems as diverse as stored program controlled telephone and data switching systems, robotic assembly lines, high speed mainframe computers, modem aircraft, local area networks, etc.
These wires provide the medium for communication signals among processing units to facilitate functionality of the whole. For example, a signal generated by a processing unit in the cockpit of an airplane is transmitted over a wire to a processing unit in the tail section to manipulate the tail control surfaces. Likewise, in a stored program controlled telephone switching office, a signal to connect a telephone call from one line to another is carried by wires interconnecting the processing units to which the telephone lines are connected.
In most stored program control systems, the “interconnecting wires” is a complex array of backplane wiring interconnecting processing units on cards, shelves of cards and cabinets of shelves. Each of these (card, shelf of cards, cabinet of shelves) may be considered a “processing unit”, because cards and shelves of related tasks are usually wired together in functional units, and then generally wired together in a cabinet. Cabinets of large stored program controlled systems are interconnected by bundles of wires (cables). Thus, the interconnecting wires provide communications paths that enable the individual processing units of the stored program controlled system to interact, thus providing the functioning of the whole.
A single change in an individual processing unit of a stored program controlled system may cause literally thousands of interconnecting wires to be moved from one processing unit to another, or connected or reconnected in some fashion. These new connections must be carefully planned and executed by skilled craftspeople who make each connection and then test it. One minor error may cause a major malfunction.
Further, these wires are bulky and are frequently grouped together into a cable bundle. Such bundling is problematic in and of itself; in that, if one or more wires in the bundle is cut, then some or all of the functionality of the stored program controlled system is lost, and it is difficult to find one damaged wire in a bundle of wires. In a worst case scenario, a single short in a bundle of wires can cause devastating fires, such as the fire in the telephone switching office in Hinsdale, Ill. in May of 1988. This fire caused a nationwide disruption of telephone service that lasted for a few days and interruption of local telephone service that lasted for several months.
Over the past decade, some interconnecting wire has been replaced by fiber optical cable. This was an advance in the art, because more signals (higher bandwidth) are carried over a smaller physical cross-section. However, fiber optics has been treated for the most part like another wire: each fiber connects one processing unit to another, the optical signal is converted between optical and electrical signals at each terminus, and the electrical signals are processed in the usual fashion.
Therefore, a problem in the art is that processing units in a stored program controlled processing system are interconnected by extensive wiring which is difficult to install, maintain and modify.